1. Field of the Invention
The present invention relates to a chair, particularly a work chair, including a mounting plate for fastening a seat and back member. The mounting plate is supported so as to be pivotable with its front end about a horizontally extending axis on a support member which is, in turn, supported by a vertical, preferably vertically adjustable, support tube and projects laterally relative to the support tube. The mounting plate is supported on its side facing away from the pivoting axis and near the seat and back member by a gas pressure spring. The gas pressure spring has at one end thereof a valve tappet for operating a valve which is integrated in the gas pressure spring, so that the effective length of the gas pressure spring is adjustable.
2. Description of the Prior Art
Chairs of the above-described type are known. In such a work chair disclosed in German Pat. No. 20 00 172, a gas pressure spring is connected to the lower end of a vertical support member. The gas pressure spring extends essentially parallel to the vertical support member. The upper end of the gas pressure spring carrying the valve tappet supports through an intermediate support member the pivotally mounted mounting plate on which the seat and back member is fastened. An essentially horizontal threaded spindle extends through this intermediate support member. By actuating the spindle, the point where the gas pressure spring acts relative to the pivotable mounting plate is adjustable. This adjusting mechanism is not only structurally very complicated. The great structural height of the mechanism makes it very difficult to create an esthetically satisfactory solution. The same is true analogously for the seat constructions known from German Offenlegungsschrift No. 25 01 673 and German Utility Model No. 73 11 376.
In order to overcome particularly the disadvantage mentioned last and to provide an adjusting mechanism of low structural height, it has already been proposed to arrange the gas pressure spring horizontally and to transmit the forces to be applied by the gas pressure spring through a lever system to the mounting plate and the seat member. This adjusting mechanism does have a low structural height, so that the underside of the chair can be constructed in a way which is pleasing to the eye. However, the lever system required for this solution is very complicated and requires a large number of components, which must be considered a disadvantage.
Another work chair of the above-described type is disclosed in U.S. Pat. No. 2,859,799. In this chair, the mounting plate carrying the seat member is supported relative to a cantilevering support member by means of a helical spring. Again, a lever system is provided between the seat member and the support member. A threaded spindle which extends through the helical spring can be used to pretension the helical spring as desired, so that the initial position to be assumed by the seat member can be adjusted. Thus, the springiness of the seat member depends upon its respective initial position. In addition, the threaded spindle required for the adjustment, or the handwheel connected to the spindle, is not easily accessible for the user of the chair. A similar construction is illustrated and described in German Offenlegungsschrift No. 20 01 097, so that the chair described therein has the same disadvantages as those mentioned with respect to U.S. Pat. No. 2,859,799.
It is, therefore, the primary object of the present invention to provide a chair of the above-described type in which the adjusting mechanism has a low structural height, so that the underside of the seat member can be constructed in an esthetically satisfactory manner and that it is ensured that the hand levers provided for adjustment can be easily reached and operated by the user of the chair while the user of the chair maintains the normal sitting position.